When the company was founded in 2007, it was about more exotic illiquid assets like mortgages, distressed debt and the like. But the heat around shares in big startups was so big that SecondMarket was happy to provide its services there, too.

It was great for PR, Silbert says, but ultimately it's a small part of the business, which handled about $5 billion of transactions last year, only $400 million of which was pre-IPO stock. The company generates about $40 million in yearly revenue now.